Set the project license in config.env; AGPL-3.0 default only for a public GitHub project

- PROJECT_LICENSE (a Gitea license key, or none) is read, checked and never asked
- Without it AGPL-3.0 applies only when GitHub is chosen and the project is public
- The license is applied on Gitea with or without GitHub, and checked against the server first
- Plan and summary name the license and where it came from
- MIL-006 accepted; README and config.env.example document the key
- Tests: new test-license.sh; existing tests use a public project where they expect AGPL-3.0

Task: MIL-006#1
Task: MIL-006#2
Task: MIL-006#3
Task: MIL-006#4
Refs #44
Refs #45
Refs #46
Refs #50

config.env.example

@@ -46,6 +46,12 @@ GITEA_API_URL=https://<your gitea instance>/api/v1
 #PROJECT_DIRECTORY=./my-project
 #ENABLE_PLAN_GATE=no                   # yes or no
 
+# Optional. The license of the project, as a Gitea license key (AGPL-3.0, MIT,
+# ...), or none for no license. It is never asked. When absent, AGPL-3.0 is
+# applied only if GitHub is used and the project is public; otherwise there
+# is no license. The Gitea server must offer the license.
+#PROJECT_LICENSE=AGPL-3.0
+
 # Optional. OWNER/NAME of the SQA-QC-Framework repository on the Gitea server;
 # it is added to the new project as a submodule over SSH.
 # Default: TirSystem/SQA-QC-Framework.